The torque output of the conventional automotive internal combustion engine is speed dependent, the output torque being maximum at a particular engine speed and falling off to some extent as the speed is either reduced or increased. This creates a range or band of engine speeds within which it is desirable to operate the engine. The conventional automotive automatic transmission is intended to maintain the engine speed within this range.
For use in the sport of drag racing, the conventional automotive automatic transmission has been modified in the past by the addition of a "trans brake". This feature allows the operator of the vehicle to stop the transfer of engine torque through the transmission to the drive shaft. With the trans brake turned on, the operator can, without using the conventional automotive brakes, drive the engine up to a desired speed. The engine loads up against the torque converter included in the transmission so that when the trans brake is released, the vehicle will be driven forward at high acceleration.
In the past, the addition of the trans brake feature to an automatic transmission has involved the installation of a solenoid valve that, when electrically actuated, establishes a second power transmission path through the gear set of the transmission in addition to that set by the usual manual gear selector. When the solenoid power shuts off, the valve returns to a normal position under the influence of a spring. This system is difficult to install. In addition, the solenoid valve is subject to sticking. While the sticking problem could be solved through use of a heavier spring, this also requires greater force from the solenoid coil in order to set the trans brake against the spring force. With a conventional 12 volt automotive system, the requisite power is not available so that relatively light springs and the consequent sticking problems have been endured.
The objective of the present invention is to provide a simpler, more effective trans brake system.